In manufacturing electronic devices, a processing may be performed on a region made of silicon oxide (SiO2) to form openings (e.g., holes or trenches) in some cases. In such a processing, a workpiece is generally exposed to plasma of a fluorocarbon gas, so that the region is etched, as described in U.S. Pat. No. 7,708,859.
Further, a technique for selectively etching a first region made of silicon oxide to a second region made of silicon nitride has been known. As an example of the technique, a self-aligned contact (SAC) technique has been known. As for the SAC technique, see Japanese Patent Laid-Open Publication No. 2000-307001.
A workpiece, which is a processing target of the SAC technique, includes a first region made of silicon oxide, a second region made of silicon nitride, and a mask made of a predetermined material. The second region is provided to define a recess, the first region is provided to fill the recess and cover the second region, and the mask is provided on the first region and provides an opening above the recess. In the conventional SAC technique, as described in Japanese Patent Laid-Open Publication No. 2000-307001, in order to etch the first region, plasma of a processing gas containing a fluorocarbon gas, oxygen gas, and a noble gas is generated, and the workpiece is exposed to active species of fluorine and/or fluorocarbon. Thus, the first region is etched in a portion exposed from the opening of the mask, so that an upper opening is formed. Further, since the workpiece is exposed to the active species, the first region in a portion surrounded by the second region, that is, in the recess, is etched in a self-aligned manner. Thus, a lower opening continuous with the upper opening is formed in a self-aligned manner.